Software Defined Radios (SDRs) methodology is rapidly gaining favor as a way to architect and design radio communication systems with greatly improved interoperability and ability to accommodate future waveform variants. SDR refers to wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence. To select the desired modulation type, the proper programs are run by microcomputers that control the transmitter and receiver. A typical voice SDR transmitter, such as may be used in mobile two-way radio or cellular telephone communication, include the following stages, where items followed by asterisks represent computer-controlled circuits whose parameters are determined by the programming (software): (1) Microphone; (2) Audio amplifier; (3) Analog-to-digital converter (ADC) that converts the voice audio to digital data*; (4) Modulator that impresses the digital intelligence onto a radio-frequency (RF) carrier*; (5) Series of amplifiers that boosts the RF carrier to the power level necessary for transmission; and (6) Transmitting antenna. A typical receiver designed to intercept the above-described voice SDR signal may employ the following stages, essentially reversing the transmitter's action, where items followed by asterisks represent programmable circuits: (1) Receiving antenna; (2) Superheterodyne system that boosts incoming RF signal strength and converts it to a lower frequency; (3) Demodulator that separates the digital intelligence from the RF carrier*; (4) Digital-to-analog converter (DAC) that generates a voice waveform from the digital data*; (5) Audio amplifier; and (6) Speaker, earphone, and/or headset. The most significant asset of SDR is versatility. Wireless systems employ protocols that vary from one service to another. Even in the same type of service, for example, cellular telephones, the protocol often differs from country to country. A single SDR set with an all-inclusive software repertoire may be used in any mode, anywhere in the world. Changing the service type, the mode, and/or the modulation protocol involves simply selecting and executing the requisite computer program. The ultimate goal of SDR engineers is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax, wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well.
With a growing demand for wireless applications and the fixed RF spectrum, research programs such as Defense Advanced Research Projects Agency (DARPA)'s next Generation (XG) are examining the possibility of re-application of spectral resources in an ad hoc manner by sensing current usage and temporarily claiming unused portions of the RF spectrum. To date, programs have proposed or demonstrated a limited set of waveforms for application on XG. However, with the emergence of SDRs, the possibility exists not only for detection of spectral re-use opportunities and filling with a fixed or parameterized waveform such as Orthogonal Frequency Division Multiplexing (OFDM) or the like, but also for selection of more comprehensive waveform characteristics such as modulation, channel coding, and TRANsmission SECurity (TRANSEC) algorithms.
Quint Networking Technology (QNT) is a DARPA-led technology program to produce a very small and modular digital communications system for a variety of ground and airborne applications. QNT may be used by dismounted air controllers and incorporated into weapons and small unmanned air vehicles (UAVs) so that these platforms may network with tactical aircraft and unmanned combat air vehicles (UCAVs) in order to better synchronize airborne and ground activities, as well as provide enhanced targeting information. The program may combine hardware miniaturization and special software to enable ad hoc bandwidth allocation to meet the dynamic demands of combat operations. The program may be targeting connectivity between dismounted soldiers, small UAVs, tactical UAVs, weapons, and manned aircraft. Low power, small size, link robustness, high throughput, low latency, mobility and ad-hoc connectivity are driving requirements for the QNT system. QNT may bring historically disadvantaged users and platforms into the Global Information Grid (GIG) as active participants and extends new levels of capability to disposable low cost radios.
One key to QNT success is to maintain highly dynamic ad hoc operation such as is accomplished with Tactical Targeting Network Technology (TTNT)/TTNT SFF (Small Form Factor) while operating for long periods of time in a low power, small form factor, battery powered device over significant distances. However, it has not been provided such a means for selection of waveform properties and parameters, which may optimally utilize the vacant portions of the spectrum in terms of their RF propagation characteristics. Further, no work has been done with respect to application of these waveforms under current spectral allocations such as Department of Defense Form 1494 (DD 1494) or the like.
Thus, it is desirable to provide a capability for examination of the vacant spectrum and selection of waveforms with characteristics which may optimally utilize the available RF characteristics while matching the demanded classes of service.